59 o SCIENCE PROGRESS 



marine animals of economic interest ; their food, reproduction, 

 and migrations ; and the connection between the invertebrate 

 population of the sea and the associated fish fauna. Lastly 

 there were the statistical studies based on the fishing experi- 

 ments made by the exploring vesels, or on the commercial 

 statistics collected by the various fishery authorities in the 

 North Sea countries. It is not to be wondered at that the 

 value of each of these lines of research was differently appraised 

 by the fishery people of the participating countries. The 

 Scandinavian investigators laid much stress on the hydro- 

 graphical researches not only from the point of view of the 

 fisheries, but also from that of the assistance which such studies 

 were likely to afford for the forecasting of weather changes. 

 The Germans and Danes were more inclined to emphasise 

 the value of the biological investigations into the life histories 

 of fishes and other animals. Then in both England and 

 Scotland particular attention was paid to statistical studies, 

 as for instance the results of the fishing voyages of the 

 exploring vessels and the commercial statistics of the fishing 

 fleets. These have been worked up with the view of elucidating 

 the movements of the fish shoals. There is, of course, much 

 room for difference of opinion as to the relative merits of each 

 of these lines of research, but one is safest in coming to the 

 conclusion that each is essential and that none can be omitted 

 if we wish really to understand the problems connected with 

 the sea fisheries ; and none can be neglected without serious 

 detriment to the lasting value of the results hoped for in the 

 end. 



Hydrographical investigation did not begin with these 

 international researches. Long ago, during the voyage of the 

 Challenger in 1872-6 a great number of observations were 

 made in the seas of the globe, and later on, in both Sweden 

 and in Scotland, a considerable amount of work of this kind 

 was effected. But it is safe to say that until the development 

 of the methods of the last half-dozen years all such work was 

 more or less imperfect and likely to lead to erroneous con- 

 clusions. It was essential that the hydrographical observa- 

 tions should be made simultaneously over wide areas, and by 

 instruments and methods the accuracy of which was beyond 

 reproach. What is actually done in these investigations is 

 to determine the temperature of the sea at different levels 



